(1) Field of the Invention
The present invention relates to an image formation apparatus, such as a laser beam printer or copying machine having a fixing unit which is removably provided for the apparatus body. (2) Description of the Prior Art
In an image formation apparatus such as a copying machine having a fixing unit removably provided for the apparatus body, a frame mechanism is well-known to separate one frame from another vertically for various purposes. The mechanism has been proposed, for example, in Japanese Utility Model Application Laid-Open No. 61-50296.
Such a conventional copying machine is constructed as shown in FIGS. 1 and 2. Namely, an image formation apparatus body 1 includes a fixing unit removably provided therein, and comprises a lower frame 2 and an upper frame 4 which is pivotally supported about a spindle 3 to open and close with respect to the lower frame 2.
The upper frame 4 comprises a photosensitive drum unit 6 and developer unit 7 serving as image formation units 5, which are removably mounted on the upper frame 4. The upper frame 4 further comprises an optical unit 8 above the image formation units 5.
The lower frame 2 comprises a fixing unit 9 removably mounted on the lower frame 2, a transfer paper cassette 10, a feed route 14 to feed a paper through a charge transferring unit 13 to the fixing unit 9, and an ejection route 17 to eject the paper through an ejection roller 15 to a tray 16.
The respective image formation units 5, i.e., the photosensitive drum unit 6, the developer unit 7 and the fixing unit 9 are consumable, and should be exchanged. For exchange of these units, the frame 4 is pivotally opened about the spindle 3 with respect to the lower frame 2 in response to operation of an opening/closing lever 18 mounted on the upper frame 4. In this condition, the photosensitive drum unit 6 and developer unit 7 can be pulled out of the upper frame 4, and exchanged. The fixing unit 9 in the lower frame 2 can be also pulled up to exchange. When a paper jam occurs, the upper frame 4 is opened as in the case of the exchange so that a jammed transfer paper 11 is removed out of the feed route 14 or ejection route 17 on the lower frame 2.
However, there are several drawbacks if exchange the image formation units 5 with the upper frame 4 opened. First, the upper frame 4 is not rigidly supported so that instability of the upper frame 4 prevents easy exchange operation.
In addition, it is difficult to pull the fixing unit 9 out of the lower frame 2 due to a small open angular between the upper and lower frames 4, 2. If the open angular becomes greater, some other problems occur. Namely, toner is spilled out of the developer unit 7 of the upper frame 4 and makes the frames below dirty. A mechanism for maintaining the opened condition, such as a strong spring assembly or lock mechanism, complicates a construction of the apparatus. Further, when pulling up the fixing unit 9 and upper frame 4 at the same time, sufficient stability of the image formation apparatus body 1 might be lost because center of gravity of the apparatus is transferred toward the back of the upper frame 4.